Some gaseous molecules (CO2, CH4, O3, N2O, chlorofluorocarbons) are known to cause climate change and increase pollution (NOx, O3, SO2, H2S) in the atmosphere. Measuring the stable isotopes of these gases can provide information about their origin, can differentiate these gases in various settings (e.g. CH4 produced from a wetland or a pipeline leak), and can help track them through production/processing scenarios or through biological and/or chemical and/or physical pathways.
Determining ratios of stable isotopes of CO2 (12CO2, 13CO2) and other greenhouse gases (methane (CH4), nitrous oxide (N2O), for example) is used for determining the source(s) of these gases. A challenge with measuring stable isotope ratios is measuring the minor isotopic species because the minor species may be present in very small amounts. The natural abundance of 13CO2 in atmospheric CO2, for example, is only approximately 1.1%; the rest is 12CO2. FIG. 1 shows ranges in isotopic variation of CO2 from sources including natural gas, plants and microbes, air, magmatic sources, petroleum, and groundwater.
Current measurements of δ13C (i.e. the carbon isotope ratio of 13C/12C within the CO2 of an unknown sample relative to a standard which is a limestone from the PeeDee formation (PDB)) involves collecting samples at the site and delivering them to the laboratory where they are analyzed using by optical spectroscopy using a commercially available absorption instrument, or by mass spectrometry with a highly precise sector mass spectrometer. The optical approach suffers from the limitations of any approach associated with collecting samples, including the lack of in situ detection. The optical approach also requires high electrical power and a continuous source of cryogens, and is thus severely limited by its continuous user interface and maintenance requirements.
Detecting CO2 seepage from a geologic storage system is difficult to do using CO2 concentration alone. Typically, other trace gases like CH4, inert tracers like perfluorocarbons, or natural tracers like the isotopes of CO2 (13C/12C and 14C/12C ratios) are used to identify CO2 leaks at the ground surface. Current efforts focusing on stable isotope identification of CO2 seepage has focused on point measurements using traps that limit both the temporal and spatial resolution of the leak. Efforts have been made in creating systems that can be used in the field to conduct real time isotope measurements at a higher temporal frequency. Systems that can resolve isotopes over 5 to 15 minute windows of time are usually bulky, expensive, and not portable.
Stable isotopes (e.g. 13C) are important for monitoring carbon sequestration potential in geologic CO2 storage systems. Point source measurements are all that can be made at this time, but remote-sensing tools that will provide spatial analysis of CO2 sources is what is needed. Furthermore, there is a need for a technology that can also provide information about where the CO2 came from.
An object of the invention is a portable system and method for continuously monitoring stable isotopes of gas.
Another object of the invention is a portable system and method for continuously monitoring CO2.
Another object of the invention is a system and method for making in-situ measurements of stable isotopes of various gases.
Another object of the invention is a system and method for making remote measurements of stable isotopes.
Another object of the invention is a system and method for making real time measurement of stable isotopes of atmospheric gases.